Hitherto, various resin compositions have been used in order to obtain electronic components such as laminated plates and printed wiring boards. For example, in multilayer printed wiring boards, resin compositions are used for forming insulation layers to insulate interlayers located internally, and for forming insulation layers located on surface layer portions. The insulation layers generally have wiring, formed by a metal layer, laminated on the surface thereof.
In addition, for the purpose of reducing the thermal expansion coefficient, inorganic fillers are often blended in the resin compositions. In recent years, associated with increasing performance and miniaturization of electronic equipment, further miniaturization of wiring and further reduction of the thermal expansion coefficient in the insulation layers are demanded also for the electronic components. In order to respond to such a demand, a large amount of inorganic fillers are sometimes blended in the resin compositions for forming the insulation layers.
As one example of the resin compositions, Patent Literature 1 described below discloses a resin composition containing an epoxy resin, a curing agent, a phenoxy resin, and an inorganic filler having a mean particle diameter of 0.01 to 2 μm. Furthermore, Patent Literature 1 also discloses a resin composition containing an epoxy resin, a curing agent, and an inorganic filler having a mean particle diameter of 0.1 to 10 μm.
In Patent Literature 1, each layer in a multilayer film having a two-layer laminated structure is formed using the above described two different types of resin compositions. It is disclosed that the multilayer film is favorably embedded in gaps and the like provided on the substrate.
Patent Literature 2 described below discloses an insulating resin material containing a curable resin, an inorganic filler, and a curing accelerator. The inorganic filler contains at least two types of fillers having different volume mean particle diameters. The particle diameter of a particle (b1) having a small particle diameter is 0.01 to 1.0 μm, and the particle diameter of a particle (b2), whose particle diameter is smallest next to the particle (b1), is 0.30 to 10 μm. When the particle (b1) and the particle (b2) are compared, the ratio of volume mean particle diameters is 1/2 to 1/100 and the ratio of weight content is 90/10 to 10/90. At least one of the particle (b1) and the particle (b2) is surface-treated with a silane coupling agent.